Temperature, electrolyte leakage, ascorbic acid content and sunscald in two cultivars of pepino, Solanum muricatum

Ripening fruit of pepino (Solanum muricatum) are susceptible to sunscald. We studied the effects of the sun over 6 d in detached mature-green fruit of cultivars 'Puzol' (used in salads) and 'Sweet Long' (used in desserts) from a summer 2001 greenhouse crop in Valencia, Spain. In both cultivars, severe sunscald symptoms developed and the skin turned yellow and brown and papery thin, while the flesh softened and browned. Infrared thermography of fruits showed that 'Puzol' is hotter in the sun (44.5 degreesC) than 'Sweet Long' (44.1 degreesC) and that maximum surface temperature increased 1 K over the 6 d. The mesocarp in the exposed part of the fruit (M1) was 2.2 K warmer than in the shaded part (M2). Average electrolyte leakage (EL) increased from 70.3% to 76.2% with sun exposure, and was as a mean higher in 'Sweet Long' (76.4 %) than in 'Puzol' (69.3 %), and in M1 (73.9 %) than in M2 (71.7 %). Ascorbic acid content (AAC) decreased over the 6 d, especially in 'Sweet Long' (from 22.0 to 7.8 mg 100 g(-1)) and in M1 (from 17.8 to 3.6 mg 100 g(-1)). Higher EL and lower AAC after exposure in M1 (78.1 % and 3.6 mg 100 g(-1), respectively), compared with M2 (74.4 % and 10.6 mg 100 g(-1)), indicate that small differences in temperature with sun exposure affect the mesocarp. Changes in AAC reflect damage (r=-0.71) more than changes in EL (r=0.49). Milder symptoms of sunscald in M2 than in M1 suggest that temperatures above 40-42degreesC are necessary for inducing severe sunscald symptoms.